Method of manufacturing oxide cathodes and cathodes manufactured by such methods



July 30, 1963 H. J. LEMMENS ETAL 3,099,577

METHOD OF MANUFACTURING OXIDE CATHODES AND CATHODES MANUFACTURED BY SUCH METHODS Filed Aug. 24, 1960 Pascm/m-rso LA YER 0/ BA -$RC0 mva 450w A6 60 INVENTORS. HENDR/KUS J LEMMENS ALBERTus VENEMA P/ETER ZAL AGENI United States Patent METHOD OF MANUFACTURING OXIDE CATH- ODES AND CATHODES MANUFACTURED BY SUCH METHODS Hendrikus Johannes Lemmens, Albertus Venema, and Pieter Zalrn, Eindhoven, Netherlands, assignors to North American Philips Company, Inc, New York, N. a corporation of Delaware Filed Aug. 24, 1960, Ser. No. 51,516 5 Claims. (Cl. 117-424) This invention relates to methods of manufacturing oxide cathodes wherein a carrier consisting substantially of nickel has provided on it a layer of alkaline-earth carbonates to which a compound of 'a noble metal has been added. The invention also relates -to cathodes manufactured by such methods.

It has been known to add, for example, ammonium platinum chloride to coating material for cathodes. The addition was effected substantially for the purpose of improving the electric conductivity of the oxide layer. With regard to the prior art existing at that time, the properties of oxide cathodes have been improved so much that for the majority of ordinary amplifying tubes there is no need of much improvement.

However, for cathodes such as used, for example, in television display tubes, continuous loadability with a high current density is a wish which cannot substantially be fulfilled by any cathode type of low cost.

According to the invention, in a method of manufacturing an oxide cathode wherein a carrier consisting substantially of nickel has provided on it a layer of alkalineearth carbonates to which a compound of a noble metal is added, a small amount of silver carbonate is added to the alkaline-earth carbonates, whereupon the cathode is finished in the usual manner. The addition is preferably effected by co-precipitation of alkaline-earth carbonate and silver carbonate.

Cathodes manufactured by a method according to the invention permit continuous current densities of 1 =amp./ cm. and higher for more than 1000 hours. A possible explanation of this fact might be found in the silver being incorporated into the lattice of the alkaline-earth oxides, resulting in the energy levels in the grains being disturbed to an extent such that a larger amount of barium can be adsorbed than would be possible in the absence of such disturbance. Due to the improved adsorption of the barium, the emission current is greater.

In order that the invention may be readily carried into effect, it will now be described in detail with reference to the drawing showing a sectional view of a cathode according to the invention and the example following hereinafter.

A tubular base of ordinary cathode nickel 1 containing 0.06% Al, 0.05% Fe 0.03% Ti has sprayed onto it a layer 2 of barium-strontium carbonate (55 %45%) with which 1% of silver carbonate has been deposited. Other compositions are 40% Ba, 40% Sr, Ca carbonate. The deposition is done from a solution of barium-strontium nitrate to which 1% of silver nitrate has been added. Deposition is done with the aid of ammonium carbonate. The quantity of silver compound may vary from 0.5 to 3%. The nickel should always contain active agents and may instead of the above given agents contain 0.6 Fe, 0.1 Mn.

The activation schedule of these cathodes which reach their normal temperature of 780 C. at a heater voltage of 6.3 v. is as follows. While the tube is continuously pumped the heater voltage is kept at 7.5 v. (about 950 C.) until the pressure is below 5 microns of mercury column. Then the heater voltage is kept at 8.5 v. (about 1050 C.) for one minute and at 10 v. (about 1120 C.) for another minute. Thereafter the heater 3 is held at 8 v. until the cathode delivers 4 a./cm. The tube is taken from the pump and the heater held at 7 v. for two hours.

What is claimed is:

1. A method of manufacturing a cathode for an electron discharge tube comprising the steps, coprecipitating alkaline earth carbonates and silver carbonate to form a layer of said alkaline earth carbonates containing about 1% of silver carbonate on a base constituted of nickel and an active agent selected from the group consisting of Al, Fe, Ti and Mn, and activating the so-coated nickel base in an evacuated discharge tube.

2. A method of manufacturing a cathode for an electron-discharge tube comprising the steps of depositing on a base constituted of nickel and an active agent selected from the group consisting of Al, Fe, Ti, and Mn a layer of alkaline earth carbonates containing about 1% of silver carbonate, and activating the so-coated base in an evacuated discharge tube.

3. A method of manufacturing a cathode for an electron-discharge tube comprising the steps of depositing on a base constituted of nickel containing about 0.06% Al, about 0.05% Fe, and less than 0.03% Ti a layer consisting of about of barium carbonate, about 45% of strontium carbonate, and about 1% of silver carbonate, and activating the so-coated base in an evacuated discharge tube.

4. A cathode for an electron discharge tube comprising a base constituted of nickel and an active agent selected from the group consisting of Al, Fe, Ti, and Mn having a layer thereon of alkaline earth carbonates containing about 1% of silver carbonate.

7 5. A cathode for an electron discharge tube comprising a base consisting of nickel containing about 0.06% of A1, about 0.05% of Fe, and less than 0.03% of Ti and a layer thereon of bariumstrontium carbonate containing about 1% of silver carbonate.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF MANUFACTURING A CATHODE FOR AN ELECTRON DISCHARGE TUBE COMPRISING THE STEPS, COPRECIPITATING ALKALINE EARTH CARBONATES AND SILVER CARBONATE TO FORM A LAYER OF A SAID ALKALINE EARTH CARBONATES CONTAINING ABOUT 1% OF SILVER CARBONATE ON A BASE CONSTITUTED OF NICKEL AND AN ACTIVE AGENT SELCECTED FRM THE GROUP CONSISTING OF AL, FE, TI AND MN, AND ACTIVATING THE SO-COATED NICKEL BASE IN AN EVACUATED DISCHARGE TUBE. 